Re: [paho-dev] Sample for Publishing multiple MQTT messages asynchronous

[Guilherme Maciel Ferreira <guilherme.maciel.ferreira@xxxxxxxxx>]

Hi,

If I'm not wrong, only one callback is called at a time by the
library. Like you noticed, the OnSend() will get called only after
OnConnect() returns. In other words, the callbacks are asynchronous
regarding your application, but synchronous in respect to the library.

I guess you should treat the callbacks like signal handlers. And you
should update state variables within them. Move loops to other
functions and leave the callbacks do the minimum work. The
paho_c_pub.c sample demonstrates it, but using a disconnect flag
[https://github.com/eclipse/paho.mqtt.c/blob/master/src/samples/paho_c_pub.c#L285-L290].
Maybe you can use the same principle to wait for the connection
establishment. It seems you want to wait to establish a connection
before send any messages, right?

Best regards,

2016-06-28 12:02 GMT-05:00 test check <testingcheck00@xxxxxxxxx>:
> Hi,
>
> I have put my hands on to MQTT recently and trying samples to achieve my use
> case.
>
> Use case : Publish messages received from another module in asynchronously
> as and when it receives to the same topic (something like message will be in
> queue and client has to read from it).
>
> I have gone through the sample in
> 'http://www.eclipse.org/paho/files/mqttdoc/Casync/publish.html' and few
> others as well. When trying to convert this example to handle multiple
> messages I had few problems on managing the callbacks within loops. Lets say
> after establishing connection, it calls 'OnConnect' callback where we send
> message and again it inturn calls another 'OnSend' callback.
>
> Problem is I tried putting a infinite loop in 'OnConnect' and send multiple
> messages but in that case when will it call 'OnSend' as it lies completely
> here.
>
> Following is the code snippet
>
> void onConnect(void* context, MQTTAsync_successData* response)
>
> {
>
>  MQTTAsync_responseOptions opts = MQTTAsync_responseOptions_initializer;
>
>  MQTTAsync_message pubmsg = MQTTAsync_message_initializer;
>
>  int rc;
>
>
>
>  opts.onSuccess = onSend;
>
>  opts.context = client;
>
>  pubmsg.payload = PAYLOAD;
>
>  pubmsg.payloadlen = strlen(PAYLOAD);
>
>
>
>  pubmsg.qos = QOS;
>
>  pubmsg.retained = 0;
>
>  deliveredtoken = 0;
>
>
>
>  int count = 0;
>
>  int messageCnt = 10;
>
>
>
>
>
>  while (count != messageCnt)
>
>  {
>
>   count++;
>
>   std::string message = "Telemetry Data #MSG_";
>
>   std::ostringstream outputString;
>
>   outputString << count;
>
>   message += outputString.str();
>
>
>
>   pubmsg.payload = malloc(message.size() + 1);
>
>   strcpy_s((char *)pubmsg.payload, message.size() + 1, message.c_str());
>
>   pubmsg.payloadlen = message.length();
>
>
>
>   if ((rc = MQTTAsync_sendMessage(client, TOPIC, &pubmsg, &opts)) !=
> MQTTASYNC_SUCCESS)
>
>   {
>
>    printf("Failed to start sendMessage, return code %d\n", rc);
>
>    exit(-1);
>
>   }
>
>  }
>
> }
>
> void onSend(void* context, MQTTAsync_successData* response)
>
> {
>
>                 MQTTAsync client = (MQTTAsync)context;
>
>                 MQTTAsync_disconnectOptions opts =
> MQTTAsync_disconnectOptions_initializer;
>
>                 int rc;
>
>                 printf("Message with token value %d delivery confirmed\n",
> response->token);
>
> }
>
>
>
> OnSend callback never called until this while loop exits and in practical it
> may be infinite loop so in that case how I will identify the successfully
> delivered are not
>
> Hence request someone to provide some samples for handling multiple messages
> publish.
>
>
>
> Regards,
>
> Senche
>
>
>
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-- 
Guilherme Maciel Ferreira
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